Systems and methods for performing the bacterial disinfection of a fluid using point radiation sources

ABSTRACT

A system for disinfecting a fluid, including: a flow cell including one or more inlet ports and one or more outlet ports, wherein the flow cell is configured to communicate a fluid containing a biological contaminant from the one or more inlet ports to the one or more outlet portions through an interior portion thereof; and one or more point radiation sources disposed about the flow cell, wherein the one or more point radiation sources are operable for delivering radiation to the biological contaminant; wherein an interior surface of the flow cell is operable for reflecting the radiation delivered to the biological contaminant by the one or more point radiation sources; and wherein the interior surface of the flow cell is operable for reflecting the radiation delivered to the biological contaminant by the one or more point radiation sources such that a radiation intensity is uniform throughout the interior portion of the flow cell. In one exemplary embodiment, the flow cell is an integrating sphere. Optionally, the system also includes a photocatalyzing material disposed on at least a portion of the interior surface of the flow cell.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present non-provisional patent application/patent claims the benefitof priority of U.S. Provisional Patent Application No. 61/139,022, filedon Dec. 19, 2008, and entitled “BACTERIAL DISINFECTION UNIT,” thecontents of which are incorporated in full by reference herein.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in the present invention andthe right, in limited circumstances, to require the patent owner tolicense to others on reasonable terms as provided for by the terms ofAward Nos. 0740524 and 0848759 awarded by the National ScienceFoundation (NSF).

FIELD OF THE INVENTION

The present invention relates to systems and methods for performing thebacterial disinfection of a fluid using point radiation sources andencompasses the fields of optical engineering, fluid engineering,materials engineering, and the biological sciences.

BACKGROUND OF THE INVENTION

Conventionally, the bacterial disinfection of fluids, such as water,air, fuel, other liquids and gases, and the like, is performed usingultraviolet (UV) lamps (or deep-UV lamps), such as low to mediumpressure mercury lamps. For example, water may be disinfected using suchlamps, for a germicidal effect, in a conventional point-of-use (POU)water filtration system. The deoxyribonucleic acid (DNA) of bacteria,viruses, cysts, and the like absorbs the UV radiation and thereproductive capabilities of the biological entities are therebydeactivated. Unlike chlorinated methods of water disinfection, the UVradiation does not impact the biological stability of the water. Thus,UV assisted water filtration has become a standard practice forgermicidal benefit in water filtration systems, including the largereactors used in public water systems (PWSs), as well as the small POUwater filtration systems. Comparable bacterial disinfection systems areused in conjunction with other fluids.

These bacterial disinfection systems, however, suffer from a number ofsignificant shortcomings. First, the bacterial disinfection systems,because they use tubular UV lamps or the like, typically have high powerrequirements and large form factors, requiring that they utilize linevoltage, represent separate components from associated fluid filtrationsystems, are not compatible with smaller form factor POU fluidfiltration systems, and/or are not arbitrarily scalable. Second, thebacterial disinfection systems are inherently inefficient. The tubularUV lamps used emit photons that pass through the fluid and are absorbedby another surface or reflected once or twice and lost. The result isthat photons must continually be generated and replaced. Further, theradiation field present is not uniform. High intensity is typically usedin lamp based systems to compensate for losses and non-uniform radiationfields. Thus, what is still needed in the art is an improved bacterialdisinfection system that addresses these shortcomings and provides otheradvantages.

BRIEF SUMMARY OF THE INVENTION

Again, the present invention relates to systems and methods forperforming the bacterial disinfection of a fluid using point radiationsources. Generally, these systems and methods utilize one or more pointradiation sources that are arranged around the interior of anintegrating sphere flow-through cell, also referred to herein as aflow-through integrating sphere (FIS), or the like. Preferably, the oneor more point radiation sources are UV optical sources, and optionallythe one or more point radiation sources are deep-UV optical sources,such as semiconductor or light-emitting diode (LED) optical sources. Theone or more point radiation sources are operable to disinfect a fluidselectively exposed to them as the DNA of bacteria, viruses, cysts, andthe like in the fluid absorbs the radiation generated and reflected inthe integrating sphere flow-through cell or the like and the biologicalentities are thereby deactivated. Optionally, the interior of theintegrating sphere flow-through cell or the like is coated with aLambertian scattering material, and/or with a photocatalytic materialcapable of destroying adsorbed biological materials in the presence ofthe generated and reflected radiation, and/or with a photocatalyticcapable of generating a disinfecting agent in the presence of thegenerated and reflected radiation.

In one exemplary embodiment, the present invention provides a system fordisinfecting a fluid, including: a flow cell including one or more inletports and one or more outlet ports, wherein the flow cell is configuredto communicate a fluid from the one or more inlet ports to the one ormore outlet portions through an interior portion thereof; and one ormore point radiation sources disposed about the flow cell, wherein theone or more point radiation sources are operable for deliveringradiation to the fluid; wherein an interior surface of the flow cell isoperable for reflecting the radiation delivered to the fluid by the oneor more point radiation sources. In one exemplary embodiment, the flowcell is an integrating sphere. Optionally, the one or more pointradiation sources include one or more of one or more semiconductoroptical sources, one or more light-emitting diode optical sources, oneor more ultraviolet optical sources, and one or more deep-ultravioletoptical sources. The interior surface of the flow cell is operable forreflecting the radiation delivered to the fluid by the one or more pointradiation sources such that a radiation intensity is uniform throughoutthe interior portion of the flow cell. Optionally, the system alsoincludes one or more mechanical baffles or stirring mechanisms disposedwithin the interior portion of the flow cell for selectively modifying aflow of the fluid therethrough. Optionally, the system further includesa photocatalyzing material disposed on at least a portion of theinterior surface of the flow cell. Optionally, the system still furtherincludes a photocatalyzing material disposed on at least a portion of asurface of the one or more mechanical baffles or stirring mechanisms.Preferably, the system includes a controller operable for selectivelyactivating/deactivating the one or more point radiation sources and acontroller operable for selectively controlling the residence time ofthe fluid in the interior portion of the flow cell.

In another exemplary embodiment, the present invention provides a methodfor disinfecting a fluid, including: providing a flow cell including oneor more inlet ports and one or more outlet ports, wherein the flow cellis configured to communicate a fluid from the one or more inlet ports tothe one or more outlet portions through an interior portion thereof; andproviding one or more point radiation sources disposed about the flowcell, wherein the one or more point radiation sources are operable fordelivering radiation to the fluid; wherein an interior surface of theflow cell is operable for reflecting the radiation delivered to thefluid by the one or more point radiation sources. In one exemplaryembodiment, the flow cell is an integrating sphere. Optionally, the oneor more point radiation sources include one or more of one or moresemiconductor optical sources, one or more light-emitting diode opticalsources, one or more ultraviolet optical sources, and one or moredeep-ultraviolet optical sources. The interior surface of the flow cellis operable for reflecting the radiation delivered to the fluid by theone or more point radiation sources such that a radiation intensity isuniform throughout the interior portion of the flow cell. Optionally,the method also includes providing one or more mechanical baffles orstirring mechanisms disposed within the interior portion of the flowcell for selectively modifying a flow of the fluid therethrough.Optionally, the method further includes providing a photocatalyzingmaterial disposed on at least a portion of the interior surface of theflow cell. Optionally, the method still further includes providing aphotocatalyzing material disposed on at least a portion of a surface ofthe one or more mechanical baffles or stirring mechanisms. Preferably,the method includes providing a controller operable for selectivelyactivating/deactivating the one or more point radiation sources and acontroller operable for selectively controlling the residence time ofthe fluid in the interior portion of the flow cell.

In a further exemplary embodiment, the present invention provides asystem for disinfecting a fluid, including: a flow cell including one ormore inlet ports and one or more outlet ports, wherein the flow cell isconfigured to communicate a fluid comprising a biological contaminantfrom the one or more inlet ports to the one or more outlet portionsthrough an interior portion thereof; and one or more point radiationsources disposed about the flow cell, wherein the one or more pointradiation sources are operable for delivering radiation to thebiological contaminant; wherein an interior surface of the flow cell isoperable for reflecting the radiation delivered to the biologicalcontaminant by the one or more point radiation sources; and wherein theinterior surface of the flow cell is operable for reflecting theradiation delivered to the biological contaminant by the one or morepoint radiation sources such that a radiation intensity is uniformthroughout the interior portion of the flow cell. In one exemplaryembodiment, the flow cell is an integrating sphere. Optionally, the oneor more point radiation sources include one or more of one or moresemiconductor optical sources, one or more light-emitting diode opticalsources, one or more ultraviolet optical sources, and one or moredeep-ultraviolet optical sources. Optionally, the system also includes aphotocatalyzing material disposed on at least a portion of the interiorsurface of the flow cell.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated and described herein with referenceto the various drawings, in which like reference numbers are used todenote like system components/method steps, as appropriate, and inwhich:

FIG. 1 is a schematic diagram illustrating one exemplary embodiment ofthe integrating sphere point radiation source fluid disinfection systemof the present invention; and

FIG. 2 is a schematic diagram illustrating another exemplary embodimentof the integrating sphere point radiation source fluid disinfectionsystem of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Again, the present invention relates to systems and methods forperforming the bacterial disinfection of a fluid using point radiationsources. Generally, these systems and methods utilize one or more pointradiation sources that are arranged around the interior of anintegrating sphere flow-through cell, also referred to herein as a FIS,or the like. Preferably, the one or more point radiation sources are UVoptical sources, and optionally the one or more point radiation sourcesare deep-UV optical sources, such as semiconductor or LED opticalsources. The one or more point radiation sources are operable todisinfect a fluid selectively exposed to them as the DNA of bacteria,viruses, cysts, and the like in the fluid absorbs the radiationgenerated and reflected in the integrating sphere flow-through cell orthe like and the biological entities are thereby deactivated.Optionally, the interior of the integrating sphere flow-through cell orthe like is coated with a Lambertian scattering material, and/or with amaterial that undergoes photocatalysis, thereby locally generating adisinfecting agent in the presence of the generated and reflectedradiation.

As a preliminary matter, it should be noted that the bacterialdisinfection systems and methods of the present invention areillustrated and described herein largely in connection with anapplication involving the disinfection of polished water in a commercialunder-sink water filtration unit. This specific application is exemplaryonly and should not be construed to be limiting in any manner. Thebacterial disinfection systems and methods of the present invention maybe generalized and utilized in any fluid disinfection application,including, but not limited to, the bacterial disinfection of water, air,fuel, other fluids and gases, and the like. Thus, the bacterialdisinfection systems of the present invention are robust and encompass awide variety of applications and industries. They are also scalable insize and scope.

Referring to FIG. 1, in one exemplary embodiment, the disinfectionsystem 10 of the present invention includes a flow cell 12 that takesthe form of an integrating sphere or the like. Although the integratingsphere configuration is discussed at length herein, other configurationsmay also be utilized. The key consideration is that photons arerepeatedly reflected within the flow cell 12 and that a uniformradiation field is formed for optimal disinfection with low intensitysources. Along these lines, the flow cell 12 should have substantiallycurved and concave opposed interior surfaces. To restate, the flow cell12 must not have internal “corners,” and every point on the interiorsurface should be visible from every other point on the interiorsurface. Ovoids, ellipsoids, cubes with rounded corners, etc. all fitthese criteria. The flow cell 12 is made of plastic or the like for easeof manufacturing, and, in such cases where the material is not a goodLambertian scatterer, the interior surfaces thereof are coated with aLambertian scattering material 14. Alternatively, the flow cell 12 ismade of a metallic or other reflective or coated reflective material,such as aluminum, stainless steel, copper, etc., which may be anodizedor otherwise coated with organic polymer, silicone, inorganic oxide,etc. The flow cell 12 is scalable and may have any suitable dimensions,on the order of millimeters to meters, for example.

The flow cell 12 includes at least an inlet port 16 and an outlet port18 manufactured into it that provides for the flow of a fluid 19 (i.e. aliquid or gas) from the inlet port 16 to the outlet port 18. It will bereadily apparent to those of ordinary skill in the art that multipleinlet ports 16 and/or multiple outlet ports 18 may also be utilized.Preferably, the fluid 19 is not allowed to stagnate in any portion ofthe interior of the flow cell 12 for an appreciable period of time, asdescribed in greater detail herein below, and the flow cell 12 is kept100% full at all times. Likewise, it may be desirable that the fluid 19be directed towards one or more interior surfaces of the flow cell 12,such that a disinfecting agent generated by a photocatalyzing materialmay be encountered, as also described in greater detail herein below.

In the nominal design, one or more point radiation sources 20, such asone or more UV optical sources, one or more deep-UV optical sources, oneor more semiconductor optical sources, and/or one or more LED opticalsources, are disposed within or partially or wholly through one or moreports (not illustrated) manufactured through the flow cell 12,preferably at symmetric positions. The one or more point radiationsources 20 are operable to disinfect the fluid 19 that is selectivelyexposed to them as the DNA of bacteria, viruses, cysts, and the like 22in the fluid 19 absorbs the radiation generated and reflected in theflow cell 12 and the biological entities are thereby deactivated. “Pointradiation sources” as used herein refer to small, roughly symmetricalradiation sources as compared to the other dimensions of the system.

Referring to FIG. 2, in another exemplary embodiment, the disinfectionsystem 10 of the present invention includes one or more mechanicalbaffles 24, mechanical stirring mechanisms, or the like, also optionallycoated with Lambertian scattering material 14 and/or photocatalyzingmaterial. This configuration is used to equilibrate and maximize theresidence time of the fluid 19 in the interior volume of the flow cell12. When a bacterium or the like 22 is in the interior volume of theflow cell 12, the goal is to optimize the design parameters (i.e. sizeof the flow cell 12, reflectance of Lambertian scattering material 14,residence time, and the radiant power of the one or more point radiationsources 20) to ensure that the bacterium or the like 22 receives alethal dose of UV radiation while it is in the flow cell 12.

Optionally, a photocatalytic material 14, such as titanium dioxide(TiO₂), zinc oxide, zirconium dioxide, iron oxide, aluminum oxide,Fe(III)/Al₂O₃, cerium oxide, manganese oxide, titanium silicates, metalsubstituted silicates or aluminosilicates, and any other metal oxide,mixed metal oxide, and/or metal doped/supported metal oxide substrates(e.g. gold nanoparticles supported on silicon dioxide or titaniumdioxide), or the like, may be disposed on the inner surface(s) of theflow cell 12 or otherwise integrated with these surfaces to enhance thephoto-oxidation, photo-reduction, and decontamination of contaminants ona near-field basis, including bacteria, pathogens, organic materials,halogenated compounds, biogenic compounds, metal ions, and/or biologicalagents. Alternatively, the photocatalyst material 14 could be suspendedon a non-absorbing substrate (such as a fiber or a mesoporous ormacroporous sol-gel, ormisil, polymer, or aeorogel) which occupies someof the interior region of the flow cell 12. This would provide uniformillumination of the catalyst from all directions for optimalphotocatalytic rates due to the unique highly reflective and randomizingnature of the integrating sphere surface. A flow detector (notillustrated) or the like may be used before or after the flow cell 12 toturn off the one or more point radiation sources 20 during periods of noflow to maximize the life of the one or more point radiation sources 20,and the entire system may be coupled to an appropriate computercontroller/processor (not illustrated) or the like that controls theoverall function of the disinfection system 10.

As a preliminary matter, DNA has peak absorption at about 260 nm, butthe absorption curve is broad, with the majority of UV absorptionoccurring between about 240 nm and about 280 nm. Low and medium pressuremercury lamps have emission peaks at about 253.7 nm, with mediumpressure lamps having emission peaks which are narrow and sporadicacross the peak microbicidal region of DNA. In comparison, UV LEDs havebroadband deep-UV emission and may be tailored for peak emission atabout 260 nm to provide the maximum dose more effectively than mercurylamps. The LED wavelength may be shifted by varying the percentcomposition of aluminum within the Al_(x)Ga_((1-x))N active layer of theLED. LEDs with wavelengths centered at the peak of DNA absorption arerecently commercially available. In addition, UV LEDs contain nomercury, which is extremely toxic such that discharge lamps containingmercury must be treated as hazardous waste and sent to an approvedrecycling facility when spent. Also, mercury based sources produceemission lines at about 185 nm, which results in ozone production; ozoneis corrosive and absorbs UV light, as well as being toxic. UV LEDs aremercury free solid state sources and may be manufactured to have noemission shorter than about 200 nm. In addition to being mercury free,UV LEDs have some distinct advantages over lamp sources. Lamps are bulkyand require line voltage which is undesirable in POU systems, where linevoltage is not always available where the unit would be positioned.Also, mercury lamps have a start-up delay time associated with thecreation of the plasma in the lamp envelop, which in turn heats theinert gas, which then vaporizes the mercury allowing the mercury andplasma ions to collide and excite the Hg to emission. In contrast, UVLEDs may be turned on instantly and operated at a very fast on/off dutycycle to increase their lifetime.

With regard to the exemplary integrating sphere embodiment of thepresent invention, integrating spheres are typically used by opticalscientists and spectroscopists to (1) efficiently collect light from alight source with a random radiation pattern and (2) create a diffusesource from the light so collected. This is accomplished throughmultiple reflections from the highly scattering interior walls of theintegrating sphere, which are inherently reflective or coated with aLambertian scattering material. In some cases, the collection isimportant, such as in the characterization of light bulbs. In othercases, the goal is to create a diffuse light source, such as forspectroscopy or photochemistry applications. In these applications, theinside volume of the integrating sphere is kept as empty as possible,usually containing only air. Because of the highly scattering interiorwalls, and the resulting path length enhancement, several individualshave recently proposed using the integrating sphere as an enhancedsample holder for absorption spectroscopy, and as a product forcharacterizing samples, e.g. ocean or lake water has been characterizedusing this principle. During operation, while filled with asubstantially or partially transparent medium, such as air (or water),the light intensity inside the integrating sphere is everywhere thesame, independent of direction. This is a unique feature of theintegrating sphere, provided that the optical source (or sources) aresmall in area as compared to the interior surface area of theintegrating sphere.

In conjunction with the systems and methods of the present invention, afluid containing a very small population of bacteria or the like isallowed to flow through the radiation filled integrating sphere. Thefollowing series of simple calculations demonstrates that, if theresidence time of the fluid (e.g. water) is controlled, then the watermay be disinfected using a relatively small number of commerciallyavailable UV LEDs or the like in conjunction with a properly designedintegrating sphere flow cell.

UV LEDs are a relatively recent emerging technology, and are ideallysuited for optimization using an integrating sphere, since they aresmall (e.g. microns square) as compared to the inner surface of a sphereof nominal size (e.g. 2-inch radius). Earlier UV light sources, such asmercury discharge lamps and the like, may not effectively be integratedwith an integrating sphere flow cell in this manner due to their largeform factor, among other considerations.

The nominal maximum flow rate of a kitchen sink, for example, is:

$\begin{matrix}{Q = {{2.5\; \frac{gal}{\min}} = {{10.0\; \frac{qt}{\min}} = {{9460\; \frac{ml}{\min}} = {158\; {\frac{ml}{\sec}.}}}}}} & (1)\end{matrix}$

A proposed FIS UV LED flow cell with radius R has a volume of:

$\begin{matrix}{V = {\frac{4}{3}\pi \; {R^{3}.}}} & (2)\end{matrix}$

So, if a particular flow of water Q is passing through the volume V, theaverage residence time of a particulate, such as a bacterium, is:

$\begin{matrix}{\tau = {\frac{V}{Q}.}} & (3)\end{matrix}$

It is assumed that otherwise potable water is contaminated with a verysmall population of bacteria, at a concentration of less than about onebacterium per volume of the sphere. In the exemplary embodiment of FIGS.1 and 2, the water flows upwards through the flow cell, from a roundport in the bottom of the sphere to a round port in the top of thesphere. In order to achieve a residence time for every bacterium oforder τ, it is anticipated that the flow should be disrupted somewherenear mid sphere, to slow down the relatively fast moving polar axialjet, and to sweep clean the relatively stagnant equatorial volume. Thisis illustrated in FIG. 2, by using a mechanical baffle or the like.Other methods for increasing residence time include: (1) the use ofmechanical stirring; (2) the use of mechanical stirring in conjunctionwith non-spherical “dimples” or the like strategically located in theequatorial areas of the integrating sphere, for example; (3) utilizingdirectional flow via a perforated nozzle (i.e. showerhead) or the likeat the water inlet; and (4) otherwise forcing the water to follow acircuitous path inside the sphere, by using a randomly bent tube, forexample—the tube should be made from a UV transparent material, such asquartz or the like. The preferred way to maximize residence time may beto inject the incoming fluid into the flow cell in a direction parallelto a latitude in the southern hemisphere, for example, with the outletperpendicular to the flow cell at the north pole, for example; this waythe swirling fluid fills up the flow cell evenly from bottom to top.Optimum placement of inlet, outlet, baffles, etc. may be modeled usingcomputational fluid dynamics (CFD). It should be noted that anynon-uniformities in the integrating sphere, such as holes, dimples,baffles, etc. may degrade its optical performance. Thus, successfuldevelopment of the systems and methods of the present invention requiresthe optimization of the trade-offs between residence time and idealintegrating sphere functionality.

If point radiation sources (e.g. UV LEDs) and receivers (i.e. bacteria,e.g E. coli bacteria) have areas that are small compared to the insidesurface area of the sphere, and if the LED power is φ_(s) (typicallymW), radius of the sphere is R, flow rate is Q (typically cc persecond), inner-surface reflectance of the sphere is k (%), reflectanceis Lambertian, and f is the port fraction of the holes for sources, etc.in the sphere, then the dose per unit area delivered to a receiver (suchas a bacterium) inside the sphere for each UV LED is:

$\begin{matrix}\begin{matrix}{{dose} = {\tau\left( \frac{\varphi}{A} \right)}} \\{= {\left( \frac{4\pi \; R^{3}}{3Q} \right)\left( \frac{k}{1 - {k\left( {1 - f} \right)}} \right)\left( \frac{\varphi_{s}}{4\pi \; R^{2}} \right)}} \\{= {\frac{R\; \varphi_{s}}{3Q}{\left( \frac{k}{1 - {k\left( {1 - f} \right)}} \right).}}}\end{matrix} & (4)\end{matrix}$

Assume that a dose of D=5 mJ/cm² is required for bacterial disinfection.Then the number of LEDs (N) required for a sphere of reflectance k,radius R, and negligible port fraction is:

$\begin{matrix}{N = {{\frac{3{DQ}}{R\; \varphi_{s}}\left( \frac{1 - k}{k} \right)} = {\frac{98.2}{R({inches})}.}}} & (5)\end{matrix}$

Assuming a SET UV LEDs with radiant power φ_(s)=0.5 mW at a forwardcurrent of 20 mA, k=95% for Spectralon coating the inner surface of thesphere, and Q=158 cm³/sec as above. Then the number of LEDs to achievethe required dose is:

Radius of integrating sphere Number UV LEDs required (inches) (@ 0.5 mW)2 49 3 33 4 25 5 20

It should be noted that the number of required LEDs scales with 1/R andalso with 1/φ_(s). The radiant power of available LEDs is expected toincrease over the time through continuous UV materials technologicaldevelopments. Likewise, the lifetime of UV LEDs is currently relativelyshort, on the order of about 300 hours. But LED operation may beoptimized utilizing a pulsing algorithm or the like, and this lifetimeis expected to continue to increase through continuous UV materialstechnological developments. The current generation of 0.5 mW UV LEDsconsume about 100 mW of power each, so the total required system powerfor kitchen faucet UV water disinfection unit with a sphere of 2.5-inchradius is 2.5 watts. The power consumed by UV LEDs is also expected tocontinue to decrease through technological developments. By comparison,a commercially available water disinfection unit with a conventional UVmercury lamp uses 14 watts for 3 gallons per minute of flow and a 10,000hour lamp life.

The Lambertian reflectance material must be non-toxic and highlyreflecting. The sphere may be made of metal or plastic, and coated withmetal, organic polymer, silicone, inorganic oxide, or anodized. Othermaterials are available with reasonably Lambertian characteristics, andreflectances on the order of k˜90% or more (e.g. certain aluminumcoatings).

As an enhancement to the systems and methods of the present invention,photocatalytic materials, such as titanium dioxide (TiO₂), zinc oxide,zirconium dioxide, iron oxide, aluminum oxide, Fe(III)/Al₂O₃, ceriumoxide, manganese oxide, titanium silicates, metal substituted silicatesor aluminosilicates, and any other metal oxide, mixed metal oxide,and/or metal doped/supported metal oxide substrates (e.g. goldnanoparticles supported on silicon dioxide or titanium dioxide), or thelike, may also be included inside the sphere or as part of the internalsurface of the sphere to enhance photo-oxidation, photo-reduction, andthe decontamination of water contaminants, including bacteria,pathogens, organic materials, halogenated compounds, biogenic compounds,metal ions, and/or biological agents. For any of these contaminants inwhich the direct absorbance of ultraviolet light is not possible or doesnot result in a decontamination, detoxification, or destruction of thecontaminant, the photocatalyst inside the sphere would act as the“UV-receiver” instead of or in addition to the contaminant. Upon UVexposure, the excited photocatalyst would interact with contaminants inthe water stream to purify the water. It should be noted that thisprocess may be staged with the radiation exposure process.

Because certain UV LEDs may operate in the near-UV region of theemission spectrum, germicidal effect of the titanium dioxide (TiO₂) orthe like may be exploited. Titanium dioxide, for example, absorbs thenear-UV effectively, having a wide bandgap of 3.2 eV; this absorptionresulting in a photocatalytic reaction. Absorption of UV light leads tophotoexcited electrons and holes, which are powerful reducing andoxidizing agents respectively (see eq. 6). The photoexcited holes reactwith adsorbed water to generate highly reactive hydroxy radicals (.OH,see eq. 7). Simultaneously, the photoexcited electrons readily reduceadsorbed O₂ to generate superoxide radicals (.O2-, see eq. 8). Thesereactive oxygen species (ROS), along with various side products, such ashydrogen peroxide, are believed to contribute to cell death inphotocatalytic decontamination schemes.

TiO₂ +hv→TiO₂(e ⁻ +h ⁺).  (6)

TiO₂(h ⁺)+H₂O_(adsorbed)→TiO₂+.OH_(adsorbed)+H⁺.  (7)

TiO₂(e ⁻)+O_(2 adsorbed)→O₂.⁻.  (8)

In accordance with the systems and methods of the present invention, thetitanium dioxide or the like is immobilized along the walls of thehighly reflecting integrating sphere. Fluoropolymer represents apotential matrix for coating the inside of the sphere due to its highreflectivity in the UV, its chemical inertness, and its ability toimmobilize titanium dioxide. Titanium dioxide may also be immobilizedinto other organic and inorganic coatings, or deposited by sputtering orelectron beam deposition. However, the continuous generation of reactiveoxygen species has a long-term negative effect on most immobilizationsubstrates. In one study, the photocatalytic oxidation via titaniumdioxide of a variety of polymer films and metal surfaces showed thatfluoropolymer was the only substrate that was resistant to oxidationfrom the reactive oxygen species produced upon photoexcitation oftitanium dioxide. Titanium dioxide immobilized on metal supports via afluoropolymer binder has been shown to maintain much of itsphotocatalytic activity, as demonstrated via photodecomposition of4-chlorophenol.

Experimental Discussion

Bacterial DNA is known to have peak absorption at a wavelength of 260 nmand initial bacterial log reduction rates were determined using a planararray of 5 LEDs. The LEDs were used to irradiate a Petri dish with 20 mLof water infused with an e-coli strain. This set up was used to baseline the dose received from UV LEDs to the standard mercury lamp sourcescurrently used in water disinfection. A prototype FIS was also designed,built, and tested to validate the UV dose enhancement. The FIS designcould hold about 230 mL of liquid and was fitted with 5 LEDs (Sphere 1)and 32 LEDs (Sphere 2). Mercury lamp source (λ=254 nm) dose requirementsfor 6 log reduction was found to be 30 mJ/cm². However, the NSF/ANSI55-20072 standard requires a minimum dose of 40 mJ/cm² at 254 nm forClass A point of entry (POE) or point of use (POU) UV systems. The 5-260nm LEDs Petri dish setup resulted in a greater than 6 log reduction inbacteria at a calculated dose of 61 mJ/cm², and a greater than 5 logreduction at 36 mJ/cm². When comparing the Petri dish configuration with5 LEDs exposing 20 mL of bacteria laden water versus prototype Sphere 1also with 5 LEDs exposing 230 mL of bacteria laden water, it wasobserved that the sphere prototype is capable of disinfecting 10 timesthe liquid volume of water than the Petri dish apparatus.

This comparison, along with the theoretical results, indicated that theintegrating sphere prototype configuration offers an enhancement in doseover a planar array of LEDs. It should be noted that both tests startedwith a bacterial (E. coli) concentration of approximately 1E7 CFU/mL.

A 6 log reduction in E. coli within 3 minutes was observed using sphere2 with 32 LEDs. The theoretical equations proposed predicted the numberof required LEDs to be N=33 for a certain reflectance value k, LED powerΦ, and sphere radius R. This calculation is comparable to theexperimental value of N=32 used in the prototype testing.

During testing, the sphere flow cell was mechanically mixed on a slowmoving orbital shaker while irradiating the bacteria infested water.Fluid dynamics modeling was performed to simulate water flow in thesphere for analysis of particle residence time. Two different modelswere used to investigate particle residence time and fluid flow in thesphere. Design A, the built prototype, had inlet and outlet portshorizontally aligned, while Design B had the inlet and outlet portsskewed horizontally with respect to each other. Both models had inletand outlet pipes of 0.5-inch diameter and were modeled with a volumetricflow rate of 23.2 cm³/s, giving an inflow velocity of 0.183 m/s.

Increasing the pathlength of the fluid increased the residence time ofany microorganisms in the fluid. To determine the particle residencetime, 12 zero mass particles were released through the inlet pipe of thesphere and tracked over time in order to replicate the particleresidence time (PRT) of microorganisms in the sphere. These simulationsdemonstrated Design A having a minimum PRT of 0.9 s while Design B had aminimum PRT of 1.4 s. In Design A, half of the particles were caught inan eddy current and hence not released within the first 2000 inches oftravel in the sphere. Design B on the other hand, exhibited a moreevenly distributed PRT with some particles revolving in eddy currentsbut not for longer than 50 seconds before exiting the sphere.

These results served to prove that the concept of using deep UV LEDs inan integrating sphere for water disinfection is feasible. Certificationlevel 6 log reduction of E. coli bacteria in water was demonstrated inthe integrating sphere flow cell prototype.

The ideal material set for the spherical flow through integrating spherewould be non-toxic, easily machine-able (so that portals may be made forfluid flow and optical sources), of sufficient mechanical integrity andstrength, inexpensive, leak-proof, and mass manufacturable.Additionally, the inner surface coating of the sphere should haveappropriate optical scattering properties, ideally Lambertian, and witha reflectivity of 1.0 in the deep ultraviolet. A reflectivity of 1.0 isnot achievable in practice, but certain materials are close.

The standard scattering material currently used for coating surfaces inmost deep UV applications is low density polytetrafluoroethylene (PTFE)inside a high reflectivity metal outer shell; PTFE acts somewhat as adiffuser, so high system reflectivity cannot be fully attained without areflective outer layer. For a 260 nm water disinfection flow cellapplication, aluminum or the like provides an appropriate outer shell.Low density PTFE objects are formed by a labor intensive multistepprocess of (1) pressing PTFE powder into a solid form (e.g. a cube or acylinder), (2) sintering at high temperature e.g. 500-600 degrees F.,(3) machining parts with oil-free cutting tools in a clean roomenvironment, and (4) encapsulating in a hard mechanical metal or polymershell. An integrating sphere is typically made by hollowing out a cubeof pressed and sintered PTFE. Since low density PTFE so prepared fordeep-UV scattering has a porous structure, in the proposed applicationit may act as an “organic sponge”, picking up any contaminants (e.g.minerals, trace organics) in the flowing water, and thus the opticalproperties of the sphere may be adversely affected. Nevertheless, avirgin integrating sphere flow cell made from low density PTFE providesan acceptable option in terms of optical properties, and thereforeinitial measurements made with such a device represent the entitlementof the system for a particular set of source power, source geometry, andinlet/outlet geometry. It should be noted that PTFE is also available inpaint-on solutions with organic binders such as polyvinyl alcohol,however, these material are not as good of reflectors at wavelengthsshorter than 300 nm due to absorption and degradation of the organicbinder materials. The organic binders also present toxicity concerns.

Barium sulfate (BaSO4) is also an exemplary option and is commonlyavailable in paint-on coatings which contain organic binder and solvent.Coatings from this type of material are specified to have reflectivityof 0.92 to 0.98 over the spectral range 300 nm to 1200 nm. However, fordeep-UV (i.e. 260 nm), the decreasing reflectivity of the BaSO4 and theUV absorption of the organic binder combine to make BaSO4 less suitablefor the current application.

Aluminum is a good candidate material for the entire integrating sphere,being a good reflector in the UV, i.e. better then e.g. silver or gold.Aluminum has been extensively used as a reflective material in theextreme UV (EUV, i.e. shorter than 200 nm) in satellite mirrorapplications, and after performance has degraded due to oxidation duringuse, the reflectance may be regenerated by over-coating with morealuminum. With a thin protective layer of e.g. magnesium fluoride(MgF₂), regeneration is not required, and aluminum can sustain areflectance of around 85% at 260 nm. This is typically accomplished bysputtering a thin (e.g. half wavelength) film of MgF₂ onto a micronsthick aluminum film that is deposited onto a surface like the inside ofa spherical shell. The spherical shell might be made of aluminum, and ifso the scattering can be rendered more Lambertian by roughening throughe.g. “bead blasting”, essentially sandblasting with glass beads beforethe aluminum and MgF₂ thin films are deposited. Aluminum and MgF₂ couldalso be deposited in a similar way onto the inner surface of a plasticsphere. Magnesium fluoride raises concerns with respect to its toxicity,though it is approved in certain small quantities by the FDA as e.g. abonding agent for aluminum foil. It is only slightly soluble in water.Its use as a thin solid reflector coating in this water disinfectionapplication would possibly require an extra layer of water imperviousencapsulation over the exposed MgF₂. Another possibility would be tocoat the inner Lambertian surface of an aluminum sphere with a hightemperature (e.g. 600 degree F.) primer/topcoat PTFE process. Anotherpossibility is a UV-transparent silicone hard coat on aluminum. Anotherpossibility is anodized aluminum.

Polymers are attractive materials for flexible spherical shell prototypegeometries and manufacturability, though their UV absorbance is high,and thus some kind of coating is required (e.g. aluminum, Al+MgF₂, PTFE,etc.) to achieve a Lambertian inner scattering surface. Rapidprototyping technology such as solid state stereolithography (SLA) andselective laser sintering (SLS) can be used to quickly and cheaplyconstruct hollow spherical prototypes with complex geometric featuresusing engineering thermoplastics such as Accura and Duraform (nylon),respectively. The benefit is that a large number of computer aideddesigns (CADs) incorporating various flow cell geometries, baffles,etc., can be first simulated using fluid dynamics software to optimizeflow cell residence time. Only the best performers are thus beprototyped and evaluated. These prototypes can then be used as models toset up inexpensive injection molding processed for mass manufacturingfrom other thermoplastic materials and coatings, optimized forLambertian scattering at 260 nm.

Although the present invention has been illustrated and described hereinwith reference to preferred embodiments and specific examples thereof,it will be readily apparent to those of ordinary skill in the art thatother embodiments and examples may perform similar functions and/orachieve like results. All such equivalent embodiments and examples arewithin the spirit and scope of the present invention, are contemplatedthereby, and are intended to be covered by the following claims.

What is claimed is:
 1. A system for disinfecting a fluid, comprising: aflow cell comprising one or more inlet ports and one or more outletports, wherein the flow cell is configured to communicate a fluid fromthe one or more inlet ports to the one or more outlet portions throughan interior portion thereof; and one or more point radiation sourcesdisposed about the flow cell, wherein the one or more point radiationsources are operable for delivering radiation to the fluid; wherein aninterior surface of the flow cell is operable for reflecting theradiation delivered to the fluid by the one or more point radiationsources.
 2. The system of claim 1, wherein the flow cell comprises oneor more of an integrating cavity, an integrating ellipsoid, and anintegrating sphere.
 3. The system of claim 1, wherein the one or morepoint radiation sources comprise one or more of one or moresemiconductor optical sources, one or more light-emitting diode opticalsources, one or more ultraviolet optical sources, and one or moredeep-ultraviolet optical sources.
 4. The system of claim 1, wherein theinterior surface of the flow cell is operable for reflecting theradiation delivered to the fluid by the one or more point radiationsources such that a radiation intensity is uniform throughout theinterior portion of the flow cell.
 5. The system of claim 1, furthercomprising one or more mechanical baffles or stirring mechanismsdisposed within the interior portion of the flow cell for selectivelymodifying a flow of the fluid therethrough.
 6. The system of claim 1,further comprising a photocatalyzing material disposed on at least aportion of the interior surface of the flow cell.
 7. The system of claim5, further comprising a photocatalyzing material disposed on at least aportion of a surface of the one or more mechanical baffles or stirringmechanisms.
 8. The system of claim 1, further comprising a controlleroperable for selectively activating/deactivating the one or more pointradiation sources.
 9. The system of claim 1, further comprising acontroller operable for selectively controlling the residence time ofthe fluid in the interior portion of the flow cell.
 10. A method fordisinfecting a fluid, comprising: providing a flow cell comprising oneor more inlet ports and one or more outlet ports, wherein the flow cellis configured to communicate a fluid from the one or more inlet ports tothe one or more outlet portions through an interior portion thereof; andproviding one or more point radiation sources disposed about the flowcell, wherein the one or more point radiation sources are operable fordelivering radiation to the fluid; wherein an interior surface of theflow cell is operable for reflecting the radiation delivered to thefluid by the one or more point radiation sources.
 11. The method ofclaim 10, wherein the flow cell comprises one or more of an integratingcavity, an integrating ellipsoid, and an integrating sphere.
 12. Themethod of claim 10, wherein the one or more point radiation sourcescomprise one or more of one or more semiconductor optical sources, oneor more light-emitting diode optical sources, one or more ultravioletoptical sources, and one or more deep-ultraviolet optical sources. 13.The method of claim 10, wherein the interior surface of the flow cell isoperable for reflecting the radiation delivered to the fluid by the oneor more point radiation sources such that a radiation intensity isuniform throughout the interior portion of the flow cell.
 14. The methodof claim 10, further comprising providing one or more mechanical bafflesor stirring mechanisms disposed within the interior portion of the flowcell for selectively modifying a flow of the fluid therethrough.
 15. Themethod of claim 10, further comprising providing a photocatalyzingmaterial disposed on at least a portion of the interior surface of theflow cell.
 16. The method of claim 14, further comprising providing aphotocatalyzing material disposed on at least a portion of a surface ofthe one or more mechanical baffles or stirring mechanisms.
 17. Themethod of claim 10, further comprising providing a controller operablefor selectively activating/deactivating the one or more point radiationsources.
 18. The method of claim 10, further comprising providing acontroller operable for selectively controlling the residence time ofthe fluid in the interior portion of the flow cell.
 19. A system fordisinfecting a fluid, comprising: a flow cell comprising one or moreinlet ports and one or more outlet ports, wherein the flow cell isconfigured to communicate a fluid comprising a biological contaminantfrom the one or more inlet ports to the one or more outlet portionsthrough an interior portion thereof; and one or more point radiationsources disposed about the flow cell, wherein the one or more pointradiation sources are operable for delivering radiation to thebiological contaminant; wherein an interior surface of the flow cell isoperable for reflecting the radiation delivered to the biologicalcontaminant by the one or more point radiation sources; and wherein theinterior surface of the flow cell is operable for reflecting theradiation delivered to the biological contaminant by the one or morepoint radiation sources such that a radiation intensity is uniformthroughout the interior portion of the flow cell.
 20. The system ofclaim 19, wherein the flow cell comprises one or more of an integratingcavity, an integrating ellipsoid, and an integrating sphere.
 21. Thesystem of claim 19, wherein the one or more point radiation sourcescomprise one or more of one or more semiconductor optical sources, oneor more light-emitting diode optical sources, one or more ultravioletoptical sources, and one or more deep-ultraviolet optical sources. 22.The system of claim 19, further comprising a photocatalyzing materialdisposed on at least a portion of the interior surface of the flow cell.